For example, an intake device constructed of valve units and an intake manifold defining intake air passages is known. Each valve unit has a resinous valve member for switching a flow of intake air and a resinous housing. The valve member and the housing are integrated into a unit, and then mounted to the intake air passage of the intake manifold. This kind of intake device is for example disclosed in Japanese Patent Publication No. 2003-509634 (U.S. Pat. No. 6,979,130 B1).
In such an intake device, dimensional allowances are required between the valve member and the housing and between the housing and the intake manifold so as to reduce deformation of the housing and interference of the valve member with the housing after the valve unit is mounted to the intake manifold. Therefore, gaps exist between the valve member and the housing and between the housing and the intake manifold. As a result, even when the valve member is operated to a position to close the passage, intake air is likely to leak through the gaps. Further, the air leakage results in deterioration of engine performance.
Also, dimensional tolerances between the valve member, the housing and the intake manifold are absorbed by deformation of the housing. Therefore, axes of valve members are likely to be displaced among the plural valve members. In such a case, because the valve members of the plural valve units are supported by a single shaft so as to be driven simultaneously, the shaft is warped or deformed. This may cause an increase in torque of the shaft and operation errors.